Carlson et al., 2017, Recent retreat of Columbia Glacier, Alaska: Millennial context: Geology, doi: /g

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1 GSA Data Repository Carlson et al., 2017, Recent retreat of Columbia Glacier, Alaska: Millennial context: Geology, doi: /g METHODS Marine Core Sedimentology and Chronology Marine jumbo piston core EW JC, along with its trigger core EW TC and site multi-core EW MC (60.66 N, W, 744 m water depth), were retrieved in Prince William Sound in the summer of 2004 C.E. aboard the RV Ewing. The composite cm below seafloor (cmbsf) depth scale used to align the jumbo piston, trigger, and multi-cores was determined via correlation of physical properties and geochemical data. Multi-core EW MC captures the sediment-water interface, while EW TC lost the uppermost 6 cm of the sediment column and EW JC failed to sample the uppermost 77 cm of the sediment column. Fig. DR1 shows the CT scan and gamma-ray attenuation bulk sediment density of EW JC. The deepest portion of the core is characterized by laminated sediments indicative of local bottom water hypoxia and/or anoxia, with low-density layers enriched in biogenic silica reflecting elevated primary productivity. This portion of the core is overlain with an erosive contact at 1052 cmbsf. This unit extends to 554 cmbsf and displays sedimentary structure indicative of a geologically instantaneous deposit associated with a submarine gravity flow, an interpretation supported by anomalously aged foraminiferal 14 C dates consistent with reworked sediment. We develop a chronology using C ages (Table DR1) on mixed benthic foraminifera tests in EW TC/JC. Samples were measured at University of California-Irvine and Australian National University, consistent with the methods outlined in Davies-Walczak et al. (2014). Although planktic foraminiferal preservation in the core was limited, we were able to

2 evaluate the benthic-planktic age offset at 780 cmbsf in core EW JC. This benthicplanktic age offset of 340±60 14 C years, when combined with the regional surface ocean R of 470±80 years (McNeely et al., 2006), indicates a benthic R of 810±100 years. The benthic foraminiferal 14 C ages were calibrated using this R value on the Marine13 curve (Reimer et al., 2013), and integrated with 210 Pb and 137 Cs data on EW MC (Walinsky et al., 2009) (Fig. 3d) to create an age model using the program BChron (Haslett and Parnell, 2008). The gravity flow deposit is excluded from the age model construction. Magnetic and Geochemical Analyses The magnetic parameters karm and k were measured at 1 cm intervals on u-channels at Oregon State University, the ratio of which provides a common magnetic grain-size proxy (Hatfield and Stoner, 2013). Bulk sediment geochemistry was measured by X-ray fluorescence at 1 mm resolution on EW JC and 0.2 mm resolution on EW TC and EW MC (records shown are smoothed to a decadal average) at Oregon State University following Carlson et al. (2008). Given the >1 cm a -1 sedimentation rate of our cores, these records reflect annual to sub-annual resolution prior to smoothing. Columbia and Shoup Glaciers sediments were collected from their terminal late-holocene moraines to determine sediment provenance source. These locations were chosen as they represent two end members of sediment source to the core site from either side of the Contact Fault that extends along the north side of Prince William Sound (Figs. 1B, C) (Wilson et al., 2012). Bulk glacial sediment geochemistry was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) at the University of Colorado. Bulk glacial sediment magnetic properties were measured in packed plastic cubes at Oregon State University following Hatfield et al. (2013). Results are shown in Table DR2. Dendrochronology 2

3 Dendrochronology samples were collected by increment borer and chainsaw from trees exposed (sub-fossil wood) by the recent retreat of Columbia Glacier. The calendar tree-ring dates are from the outer rings of mountain hemlock trees (Tsuga mertensiana) that have been killed by the advancing glacier, pushed against the surrounding bedrock fiord walls, and although they have been transported, most are associated with primary soils and forest debris. We determined the calendar kill dates for the sub-fossil logs by cross-dating the mountain hemlock trees to a master calendar dated tree-ring chronology for southern Alaska (Barclay et al., 2009; Wiles et al., 2014) using standard dendrochronological techniques (Stokes and Smiley, 1996). These data have been used in dendro-climatic studies (Wilson et al., 2007; Wiles et al., 2014), updated by Starr et al. (2015), and previously unpublished Columbia Glacier tree-ring dating by Kennedy (2003) appeared in Nick et al. (2007) and Barclay et al. (2009). Information on the dendrochronology samples is provided in Table DR3. Glacier Modeling Simulations of Columbia Glacier response to ambient temperature come from Colgan et al. (2012). Briefly, this flow-line model, which includes a first order approximation for longitudinal coupling stresses, was run 20,000 times in a Monte Carlo forward selection approach, whereby simulations that matched the 1980 C.E. extent and thickness of Columbia Glacier (Meier et al., 1985) at the end of spin-up to transient equilibrium were retained (n=3020). The selected simulations were then forced with different rates and durations of climate warming that changed the equilibrium line altitude until triggering Columbia Glacier retreat. The selected simulations induced retreat under a diverse range of rates and durations of climate warming (Fig. 4). We divided the selected simulations into ten bins, based on warming rate, with 302 simulations per bin. We then calculated the mean and standard deviation of the rates and durations of warming in each bin (gray bars in Fig. 4) to assess the relation between intensity of climate change (rate and duration of warming) and the instability and retreat of Columbia Glacier. We compare this against the actual rate and duration of warming in April-September air temperature, as inferred 3

4 locally over the 1871 to 2008 period by NOAA/OAR/ESRL PSD Twentieth Century Reanalysis V2, which preceded the destabilization and retreat of Columbia Glacier in the mid 1980 s C.E. (Compo et al., 2011; Colgan et al., 2012). 4

5 References Cited Barclay, D.J., Wiles, G.C., and Calkin, P.E., 2009, Holocene glacier fluctuations in Alaska: Quaternary Science Reviews, v. 28, p Carlson, A.E., Stoner, J.S., Donnelly, J.P., and Hillaire-Marcel, C., 2008, Response of the southern Greenland Ice Sheet during the last two deglaciations: Geology, v. 36, p Colgan, W., Pfeffer, W.T., Hajaram, H., Abdalati, W., and Balog, J., 2012, Monte Carlo ice flow modeling projects a new stable configuration for Columbia Glacier, Alaska, c. 2020: The Cryosphere, v. 6, p Compo, G.P., and 26 others, 2011, The Twentieth Century Reanalysis Project: Quarterly Journal of the Royal Meteorological Society, v. 137, p Davies-Walczak, M., Mix, A.C., Stoner, J.S., Southon, J.R., Cheseby, M., and Xuan, C., 2014, Late Glacial to Holocene radiocarbon constraints on North Pacific Intermediate Water ventilation and deglacial atmospheric CO 2 sources: Earth and Planetary Science Letters, v. 397, p Haslett, J., and Parnell, A., 2008, A simple monotone process with application to radiocarbondated depth chronologies: Journal of the Royal Statistical Society, v. 57, p Hatfield, R.G., and Stoner, J.S., 2013, Magnetic properties and susceptibility: Encyclopedia of Quaternary Science, v. 2, p Hatfield, R.G., Stoner, J.S., Carlson, A.E., Reyes, A.V., and Housen, B.A., 2013, Source as a controlling factor on the quality and interpretation of sediment magnetic records from the northern North Atlantic: Earth and Planetary Science Letters, v. 368, p Kennedy, M.G., 2003, Advance rates of Columbia Glacier during the last 1000 years, Prince William Sound, Alaska: College of Wooster Senior Thesis, Wooster Ohio, 45 pp. McNeely, R., Dyke, A.S., and Southon, J.R., 2006, Canadian marine reservoir ages, preliminary data assessment: Geological Survey of Canada Open File

6 Meier, M., Rasmussen, L., Krimmel, R., Olsen, R., and Frank, D., 1985, Photogrammetric Determination of Surface Altitude, Terminus Position, and Ice Velocity of Columbia Glacier, Alaska: U.S. Geological Survey Professional Paper 1258-F, 40 pp. Nick, F.M., van der Veen, C.J., and Oerlemans, J., 2007, Controls on advance of tidewater glaciers: Results from numerical modeling applied to Columbia Glacier: Journal of Geophysical Research, v. 112, doi: /2006JF Reimer, P.J., and 29 others, 2013, IntCal13 and Marine13 radiocarbon age calibration curves 0-50,000 years cal BP: Radiocarbon, v. 54, p Starr, K., Happ, M., Wiles, G., and Wiesenberg, N., 2015, Reconstructing ice dynamics from forests preserved in the wake of the catastrophic retreating Columbia Glacier, Alaska: Geological Society of America Abstracts with Programs, v. 47, p Stokes, M.A., and Smiley, T.L., 1996, An Introduction to Tree-ring Dating: The University of Arizona Press, Tucson. 73 p. Walinsky, S.E., Prahl, F.G., Mix, A.C., Finney, B.P., Jaeger, J.M., and Rosen, G.P., 2009, Distribution and composition of organic matter in surface sediments of coastal Southeast Alaska: Continental Shelf Research, v. 29, p Wiles, G.C., D Arrigo, R.D., Barclay, D., Wilson, R.S., Jarvis, S.K., Vargo, L., and Frank, D., 2014, Surface air temperature variability reconstructed with tree rings for the Gulf of Alaska over the past 1200 years: The Holocene, v. 24, p Wilson, F.H., and Hults, C.P., 2012, Geology of the Prince William Sound and Kenai Peninsula Region, Alaska: U.S.G.S. Scientific Investigation Map Wilson, R., Wiles, G., D Arrigo, R., and Zweck, C., 2007, Cycles and shifts: 1300-years of multidecadal temperature variability in the Gulf of Alaska: Climate Dynamics, v. 28, p

7 Table DR1. 14 C ages; italics ages are out of stratigraphic order. Core CAMS/ANU Sample Number Material Depth in core (cm) Depth below surface (cm) 14 C age 1 sigma Calibrated age 1 sigma 124 EW TC Benthic Post-Bomb Post-Bomb EW JC Benthic EW TC Benthic EW JC Benthic EW TC Benthic EW JC Benthic EW JC Benthic EW JC Benthic EW JC Benthic EW JC Planktonic EW JC Benthic EW JC Benthic EW JC Benthic EW JC Benthic EW JC Benthic EW JC Benthic EW JC Benthic EW JC Benthic Table DR2. Geochemistry and magnetic properties of glacial sediments Glacier Latitude Longitude Fe (ppm) Si (ppm) Ca (ppm) Si/Fe Si/Ca k karm karm/k Shoup Columbia Table DR3. Dendrochronology data with distance from the late Holocene moraine Tree Ring Series C.E. Growth ka Kill Latitude Longitude Advance (km) CG05B TC A CG EB

8 Figure DR1. CT scan false color on the left and bulk sediment density (ρ) on the right versus cmbsf in EW JC. The red box denotes the gravity-flow deposit. 129 CT Scan - false color Depth bsf (cm) (g/cm 3 ) 8